Superfluid behavior of quasi-1D p-H$_2$ inside carbon nanotube

TL;DR

This study uses quantum Monte Carlo simulations to demonstrate that para-hydrogen confined in carbon nanotubes can exhibit superfluid behavior, with the central column acting as a stable one-dimensional superfluid described by Tomonaga-Luttinger liquid theory.

Contribution

It provides the first ab-initio evidence of superfluidity in para-hydrogen within carbon nanotubes, highlighting the role of 1D confinement and Luttinger liquid behavior.

Findings

Central column of pH2 acts as a 1D superfluid

Luttinger parameter shows non-monotonic density dependence

Superfluidity is stable against weak disorder

Abstract

We perform ab-initio Quantum Monte Carlo simulations of para-hydrogen (pH$_2$) at $T=0$ K confined in carbon nanotubes (CNT) of different radii. The radial density profiles show a strong layering of the pH$_2$ molecules which grow, with increasing number of molecules, in solid concentric cylindrical shells and eventually a central column. The central column can be considered an effective one-dimensional (1D) fluid whose properties are well captured by the Tomonaga-Luttinger liquid theory. The Luttinger parameter is explicitly computed and interestingly it shows a non-monotonic behavior with the linear density similar to what found for pure 1D $^3$He. Remarkably, for the central column in a (10,10) CNT, we found an ample linear density range in which the Luttinger liquid is (i) superfluid and (ii) stable against a weak disordered external potential, as the one expected inside realistic pores. This superfluid behavior could be experimentally revealed in bundles of carbon nanotubes, where deviations from classical inertial values associated with superfluid density could be measured via torsional oscillator techniques. In summary, our results suggest that pH$_2$ within carbon nanopores could be a practical realization of the long sought-after, elusive superfluid phase of parahydrogen.